U.S. Pat. No. 5,618,903 describes polyethylene-polysiloxane block copolymers for use in release surface compositions. Such polymers and polysiloxane homopolymers and other copolymers are made by a process which utilizes a volatile hydrocarbon liquid as the solvent for anionic polymerization. This process necessarily requires an expensive solvent removal step and equipment for recycle of the solvent. Thus, it can be seen that it would be advantageous to provide a process to make block copolymers of this type which does not require the use of a volatile hydrocarbon solvent.